1. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Figure 13.1 A Molecular Representation of the Reaction 2NO 2 (g)      g) Over Time in a Closed Vessel

2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Chemical Equilibrium The state where the concentrations of all reactants and products remain constant with time. On the molecular level, there is frantic activity. Equilibrium is not static, but is a highly dynamic situation.

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Figure 13.2 Changes in Concentrations

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Figure 13.3 H 2 0 and CO Begin to React and Reach Equilibrium

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Figure 13.4 The Changes with Time in the Rates of Forward and Reverse Reactions

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 The Haber Rxn N 2 + 3H 2 → 2NH 3 all (g);

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Figure 13.5 The Ammonia Synthesis Equilibrium

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 The Law of Mass Action For jA + kB  lC + mD The law of mass action is represented by the equilibrium expression:

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Equilibrium Expression 4NH 3 (g) + 7O 2 (g)  4NO 2 (g) + 6H 2 O(g)

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Notes on Equilibrium Expressions 4 The Equilibrium Expression for a reaction is the reciprocal of that for the reaction written in reverse. 4 When the equation for a reaction is multiplied by n, EE new = (EE original ) n 4 The units for K depend on the reaction being considered. So, we will omit them!

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 K v. K p For jA + kB  lC + mD K p = K(RT)  n  n = sum of coefficients of gaseous products minus sum of coefficients of gaseous reactants.

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Heterogeneous Equilibria... are equilibria that involve more than one phase. CaCO 3 (s)  CaO(s) + CO 2 (g) K = [CO 2 ] The position of a heterogeneous equilibrium does not depend on the amounts of pure solids or liquids present.

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Figure 13.6 CaCO 3 (s) CaO(s) + CO 2 (g)

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Figure 13.7 The Difference between Thermodynamic and Kinetic Stabilities

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Reaction Quotient... helps to determine the direction of the move toward equilibrium. The law of mass action is applied with initial concentrations.

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Reaction Quotient (continued) H 2 (g) + F 2 (g)  2HF(g)

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Solving Equilibrium Problems 1.Balance the equation. 2.Write the equilibrium expression. 3.List the initial concentrations. 4.Calculate Q and determine the shift to equilibrium.

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Solving Equilibrium Problems (continued ) 5.Define equilibrium concentrations. 6.Substitute equilibrium concentrations into equilibrium expression and solve. 7.Check calculated concentrations by calculating K.

19. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Le Châtelier’s Principle... if a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce that change.

20. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Figure 13.8 A Mixture of N 2, H 2, and NH 3

21. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Effects of Changes on the System 1.Concentration: The system will shift away from the added component. 2.Temperature: K will change depending upon the temperature (treat the energy change as a reactant).

22. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Effects of Changes on the System (continued) 3.Pressure: a. Addition of inert gas does not affect the equilibrium position. b. Decreasing the volume shifts the equilibrium toward the side with fewer moles.

23. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Figure 13.9 The Effect of Decreased Volume on the Ammonia Synthesis Equilibrium